Conventionally, an ionic liquid is known as an ionic compound. The ionic liquid receives attention as a material facilitating development of a capacitor, a lithium ion battery, a fuel cell, a solar cell, and the like. The ionic liquid has low environmental load and high heat-resistance and is expected as solvents for metal plating and various reaction solvents. Further, the ionic liquid is being studied for use as a lubricant in special environments such as space development field and possibilities of using the ionic liquid are expected in many fields.
When using the ionic liquid as a solvent of a lithium ion battery, the ionic liquid is superior in terms of safety to an organic solvent such as a carbonate solvent because it does not ignite due to its nonvolatility. However, a lithium salt is dissolved in the ionic liquid for the lithium ion battery. Thus, 2 (two) cations and 2 (two) anions present in the solution and interfere with the lithium ion transfer. Taking this into consideration, polyethylene glycol (PEG) based ionic compounds including the lithium ion as the cation has been developed.
Patent document 1 discloses LiAl[O(CH2CH2O)3CH3]4 that is a colorless liquid and has an ionic conductance of 1.1×10−5 S/cm (25° C.). Patent document 2 notes an introduction of an electron withdrawing group into the PEG based ionic compound, that decreases a charge density of the anion so as to reduce an anion-cation interaction, and discloses a production example of LiAl[O(CH2CH2O)mCH3]2[OCOCF3]2 (m=3, 7.2, 11.8). In the patent document 2, LiAl[O(CH2(CH2O)mCH3]2[OCOOF3]2 is in a solid state when m=3, and in a liquid state when m=7.2 or 11.8. The patent document 2 discloses that the ionic conductance of LiAl[O(CH2CH2O)mCH3]2[OCOCF3]2 is highest when m=7.2. Further, patent document 3 discloses that the ionic conductance is favorably improved by adding Lewis acid to the PEG based ionic compound into which the electron withdrawing group is introduced. In addition, patent documents 4-8 also disclose PEG based ionic compounds.    Patent Document 1: Japanese Patent Laid-Open No. H8-301879    Patent Document 2: JP 2003-146941 A    Patent Document 3: JP 2007-115527 A    Patent Document 4: JP 2007-99706 A    Patent Document 5: JP 2007-99705 A    Patent Document 6: JP 2008-69102 A    Patent Document 7: JP 2004-307481 A    Patent Document 8: JP 2004-67554 A